The Teseo-LIV3 GPS module (as used in shabaz ' GPS / Galileo / BeiDou / GLONASS receiver) talks UART and I2C. I developed an OO driver and parser for it.
The Raspberry Pico port is now ready for a stable release.

GitHub Release 1.0, with binaries.

Overview:

• driver library for Teseo GPS (device independent)
• parser library for NMEA messages (device independent)
• UART and I2C implementation for Raspberry Pico / RP2040
• Teseo driver example (device independent, compiled for Pico)
• NMEA parser and Teseo driver example (device independent, compiled for Pico)
• I2C and UART binaries for both examples, ready to drop-and-run on your RP2040

Pico resources used only if you use I2C:

• I2C0
• SDA: GP16 (Pico I2C0 SDA)
• SCL:  GP17 (Pico I2C0 SCL)
• baud: 100 * 1000

for I2C, SDA connects to SDA and SCL to SCL. The PCB that I use has the pull-ups for I2C.

Pico resources used only if you use UART:

• UART1
• TX: GP4 (Pico UART1 RX)
• RX:  GP5 (Pico UART1 Tx)
• baud: 9600
• UART1 RX interrupt

for UART, RX connects to TX and vice versa

Pico common resources:

• RESET: GP18 (optional)
• 5V: VBUS
• 0V: GND

image: how to hook up the Teseo PCB to a Pico.

Dependency between examples, libraries and Pico / RP2040 port:

Api changes since previous version:

• the NMEA parser api is new functionality
• Teseo lib: the command / validation pair changed.
  pair.second is no longer representing the validation line (the NMEA command itself has enough info).
  new use: nmea_rr teseo::gll("$PSTMNMEAREQUEST,100000,0\n\r", "GLL,");
  The first string, the NMEA command, is unchanged.
  The second "check" string now represents the signature of a NMEA reply (and is used for that). 
  Code now uses the first string a command, and as validator for the closing validation line.

Example changes:

• new example to showcase the Teseo GPS communication lib, together with the NMEA parser lib

Infrastructure changes

• default build generates binaries for each example, in I2C and UART variant
• Pico C/C++ SDK compatible
• GitHub action scripts to validate build and create nightly releases
• Teseo and NMEA lib are subprojects that can be used in isolation
• Pico dependent code moved out of examples, into port/pico directory
• Pico I2C reader is way better and resource-friendlier in this version

Other:

• requires a C++23 capable toolchain. Developed and tested on GCC 13.3.1
• tested with Pico C/C++ SDK 1.5.1 and 2.0.0

Development examples

For the full source code of the parser example I review here, check the documentation.

Typical query - response - parse code example - query that returns a single reply:

teseo::teseo gps;
std::string reply;
bool valid; // intentionally uninitialised

// 

nmea::gll o; // NMEA GLL object
valid = gps.ask_gll(reply); // ask Teseo GPS library for GLL data
if (valid) {
    valid = nmea::gll::from_data(reply, o); // fill NMEA GLL object with the reply attributes
}

debugger view after the GLL object is built up:

Using the object in your code (print example snippet):

printf("lat: %f, lon: %f.", 
    o.lat, o.lon);

GLL source: gps. lat: 50.863354 lon: 4.376334, time: 11:00:32.000.

Typical query - response - parse code example - query that returns a multiple replies:

teseo::teseo gps;
std::vector<std::string> replies(NMEA_MAX_REPLIES); 
// vector size is a suggestion. STL will allocate at least NMEA_MAX_REPLIES
uint count; // intentionally uninitialised
bool valid; // intentionally uninitialised

// ...

valid = gps.ask_gsv(replies, count);
if (!valid) { return; }
for(auto r : std::ranges::subrange(replies.begin(), replies.begin() + count)) {
	nmea::gsv o;
    valid = nmea::gsv::from_data(r, o);
    
    // .. either use the object, or store it in a container for later use.
}

debugger view:

Using the object in your code (example where the retrieved objects are directly used for printing, not stored for later use):

	for(auto r : std::ranges::subrange(replies.begin(), replies.begin() + count)) {
		nmea::gsv o;
	    valid = nmea::gsv::from_data(r, o);
        printf("GSV source: ");
        print_talker(o.source);
        printf(".\r\n");
	    for(const auto s : o.sats) {
            printf("sat prn: %i, elev: %i, azim: %i, snr: %i.\r\n", 
                s.prn, s.elev, s.azim, s.snr);
	    }
	}

GSV source: gps.
sat prn: 3, elev: 84, azim: 344, snr: 21.
sat prn: 2, elev: 48, azim: 135, snr: 27.
sat prn: 17, elev: 48, azim: 271, snr: 25.
sat prn: 4, elev: 43, azim: 182, snr: 43.
GSV source: gps.
sat prn: 19, elev: 36, azim: 303, snr: 14.
sat prn: 21, elev: 32, azim: 133, snr: 21.
sat prn: 28, elev: 20, azim: 56, snr: 0.
sat prn: 31, elev: 20, azim: 92, snr: 0.
GSV source: gps.
sat prn: 6, elev: 16, azim: 304, snr: 0.
sat prn: 9, elev: 13, azim: 204, snr: 37.
sat prn: 49, elev: 31, azim: 179, snr: 41.
sat prn: 0, elev: 0, azim: 0, snr: 0.
GSV source: glonass.
sat prn: 84, elev: 77, azim: 311, snr: 0.
sat prn: 69, elev: 67, azim: 220, snr: 25.
sat prn: 68, elev: 56, azim: 41, snr: 25.
sat prn: 83, elev: 34, azim: 145, snr: 22.
GSV source: glonass.
sat prn: 85, elev: 20, azim: 323, snr: 0.
sat prn: 85, elev: 20, azim: 323, snr: 0.
sat prn: 77, elev: 9, azim: 34, snr: 0.
sat prn: 76, elev: 10, azim: 352, snr: 23.
GSV source: glonass.
sat prn: 67, elev: 8, azim: 41, snr: 0.
sat prn: 0, elev: 0, azim: 0, snr: 0.
sat prn: 0, elev: 0, azim: 0, snr: 0.
sat prn: 0, elev: 0, azim: 0, snr: 0.

visit the github repository (git clone https://github.com/jancumps/pico_gps_teseo.git)
view the online documentation
Link to all posts.